The present invention is directed to cooling of molds in a glassware forming machine, and more particularly to liquid cooling of the blank molds and/or blow molds in an individual section machine.
The science of glass container manufacture is currently served by the so-called individual section or IS machine. Such machines include a plurality of separate or individual manufacturing sections, each of which has a multiplicity of operating mechanisms for converting one or more charges or gobs of molten glass into hollow glass containers and transferring the containers through successive stations of the machine section. Each machine section includes one or more blank molds in which a glass gob is initially formed in a blowing or pressing operation, one or more invert arms for transferring the blanks to blow molds in which the containers are blown to final form, tongs for removing the formed containers onto a deadplate, and a sweepout mechanism for transferring molded containers from the deadplate onto a conveyor. U.S. Pat. No. 4,362,544 includes a background discussion of both blow-and-blow and press-and-blow glassware forming processes, and discloses an electropneumatic individual section machine adapted for use in either process.
In the past, the blank and blow molds of a glassware forming machine have generally been cooled by directing air onto or through the mold parts. Such techniques increase the temperature and noise level in the surrounding environment. Furthermore, productivity is limited by the ability of the air to remove heat from the mold parts in a controlled process, and process stability and container quality are affected by the difficulty in controlling air temperature and flow rate. It has been proposed in U.S. Pat. No. 3,887,350 and 4,142,884, for example, to direct a fluid, such as water, through passages in the mold sections to improve heat extraction. However, heat extraction by liquid cooling can be too rapid and uncontrolled, at least in some areas of the mold, so steps must be taken to retard heat transfer from the inner or forming surface of a mold section to the outer periphery in which the liquid cooling passages are disposed. Various techniques for so controlling liquid-cooling heat extraction have been proposed in the art, but have not been entirely satisfactory.
Mold material for manufacture of quality glassware must have the following characteristics: good wear properties, good thermal cycle resistance to cracking, good mechanical properties, good glass release properties, ease of machinability, ease of repair and economic feasibility. Ductile iron, which is defined as an iron in which free microstructural graphite is in the form of spheres, has been proposed for use as a mold material to manufacture glassware in which reduced thermal conductivity (as compared to gray iron for example) is desired. Specific examples of glassware in which ductile iron is employed as the mold material are small containers that require a small amount of heat removal in the mold equipment, such as cosmetic and pharmaceutical bottles. However, ductile iron has not been employed in manufacture of larger glassware because of its reduced heat transfer and thermal cycle resistance capabilities. Ni-Resist ductile iron has been proposed for glassware manufacture. The increased nickel content of Ni-Resist ductile iron contributes to improved glass release properties. However, standard austenitic Ni-Resist ductile iron does not exhibit desired thermal conductivity and resistance to thermal cyclic cracking.
It is therefore a general object of the present invention to provide a glassware forming mold, and a method of cooling such a mold, that improve temperature control stability at the mold forming surface. Another and more specific object of the present invention is to provide a mold and method of cooling in which mold surface temperature can be adjusted and dynamically controlled during the glassware forming operation. Yet another object of the present invention is to provide a mold and method of cooling in which more uniform temperature and temperature control are obtained both circumferentially and axially of the mold forming surface to tailor the overall heat transfer characteristics of the mold coolant system to achieve efficient glass forming. Yet another object of the present invention is to provide a mold cooling technique that is characterized by reduced corrosion in the cooling passages and improved operating life of the entire mold and cooling system. A further object of the invention is to provide a material for construction of a glassware mold, including either a blank mold or a blow mold, that exhibits the desirable mold properties listed above.
A glassware forming mold in accordance with presently preferred embodiments of the invention includes at least one body of heat conductive construction having a central portion with a forming surface for shaping molten glass and a peripheral portion spaced radially outwardly of the central portion. At least one passage extends through the peripheral portion of the mold, and liquid coolant is directed through the passage for extracting heat from the body by conduction from the forming surface. At least one opening is provided in the mold body extending into the body and positioned radially between the coolant passage and the forming surface for retarding heat transfer from the surface to liquid coolant in the passage. The mold preferably comprises a split mold having a pair of mold bodies with identical arrays of passages and openings. The mold may be either a blank mold or a blow mold.
In the disclosed embodiments of the invention, the openings have a depth into the body, either part way or entirely through the body, coordinated with contour of the forming surface and other manufacturing parameters to control heat transfer from the forming surface to the coolant passages. The openings may be wholly or partially filled with material for further tailoring heat transfer from the forming surface to the coolant passages. In a mold body having a plurality of coolant passages and a plurality of openings, the heat transfer properties of the openings may be tailored circumferentially around the mold body, such as by partially filling every other passage. Thus. the heat transfer characteristics of the mold body can be tailored both radially, axially and circumferentially of the mold to obtain desired heat transfer and forming surface temperature characteristics.
Endplates may be carried by the mold body for controlling flow of coolant in multiple passes through the coolant passages in the mold body. In the preferred embodiments of the invention, one of the endplates contains a fluid inlet and a fluid outlet, and channels for directing the fluid to the mold passages. The other endplate contains channels for routing fluid from the end of one coolant passage to the end of an adjacent passage. In the disclosed embodiments of the invention, liquid coolant makes four passes through the mold body before returning to the fluid sump. The number of passes through the mold body may vary upwardly and downwardly depending upon mold size, the amount of heat to be extracted, etc. It is also anticipated that the number of coolant passes for cooling a blank mold will be less than for a blow mold.
In accordance with yet another feature of the present invention, the liquid coolant comprises water, preferably mixed with a heat transfer fluid such as propylene glycol. Other heat transfer fluids include silicon-based heat transfer fluids, synthetic organic fluids, and inhibited glycol-based fluids. The coolant fluid control system preferably includes facility for detecting and controlling coolant composition (e.g., propylene glycol concentration), coolant temperature and coolant flow rate, and an electronic controller for controlling composition temperature and/or flow rate to achieve optimum cooling and temperature control at the mold forming surfaces. In this way, mold surface temperature can be dynamically adjusted and controlled.
In accordance with a further feature of the present invention, which may be employed either separately from or more preferably in combination with other features of the invention, the mold body or bodies are constructed of austenitic Ni-Resist ductile iron. Such ductile iron is preferably a Type D Ni-Resist ductile iron in accordance with ASTM-A439-84, but modified to possess increased silicon and molybdenum content. Type D2-C iron is currently employed. Silicon content is preferably in excess of 3.0%, and most preferably is 4.20%xc2x10.20%. Molybdenum content is preferably in excess of 0.5%, and most preferably 0.70xc2x10.10%. (All composition percentages in this application are in weight percent.) The increased silicon content decreases the thermal conductivity of the mold material. The increased molybdenum content improves thermal cycle resistance to cracking. The increased nickel content characteristic to Ni-Resist materials improves glass release properties. The austenitic Ni-Resist ductile iron mold composition in accordance with this aspect of the invention also yields desirable wear and other mechanical properties, ease of machinability and repair, and desirable economic feasibility. Austenitic ductile Ni-Resist material also provides a more stable microstructure than gray iron, for example, up to a temperature of 1400xc2x0 F.
A method of cooling a mold for a glassware forming machine in accordance with yet another aspect of the present invention contemplates providing a mold body of heat conductive construction having a forming surface, at least one coolant passage extending axially through the body, and at least one opening that extends at least part way through the body. The opening is disposed radially between the coolant passages and the mold forming surface. Liquid coolant is circulated through the passages. Heat transfer from the forming surface to the coolant is controlled in part by controlling diameter and depth of the opening, and by optionally at least partially filling the opening to modify the heat transfer characteristics across the opening. In the preferred embodiments of the invention, at least one, and preferably all of composition, temperature and flow rate of the liquid coolant are controlled.